The invention relates to a system for storing and/or reproducing information, comprising a disc-shaped record carrier and a device provided with means for writing and/or reading information in/from a track on the record carrier, which track is arranged in accordance with a spiral pattern of windings, the information being represented by marks constituted by bit cells having a bit length.
The invention also relates to a record carrier for use in such a system, which record carrier is provided with a servopattern arranged in accordance with a spiral pattern of windings indicative of a track intended for recording, the information being represented by marks constituted by bit cells having a predetermined bit length Bl.
The invention further relates to a device for writing and/or reading information for use in such a system, comprising means for writing and/or reading information in/from a track on a disc-shaped record carrier, which track is arranged in accordance with a spiral pattern of windings having a predetermined track pitch Tp, the information being represented by marks constituted by bit cells having an at least substantially constant bit length Bl, and clock means for generating a bit clock synchronously with the bit cells during scanning of the track.
A system of the type described in the opening paragraph, comprising a record carrier and a device for reading and/or writing information, is known from WO 96/34389 (PHN 15.333). The known record carrier is provided with a spiral track of windings intended for recording information blocks, in which the information is represented by a succession of optically readable marks. The mark""s are constituted by bit cells, each of which represents a channel bit via a channel code such as, for example the known EFM code in the Compact Disc (CD) and the recordable CD-R. Moreover, the record carrier is provided with a servopattern having a periodical modulation, in which disc information is coded such as, for example writing parameters. This modulation has a fixed number of periods per winding so that, based thereon, the record carrier can rotate at a constant angular velocity (CAV). The known device is provided with drive means for rotating the record carrier and with a read and/or write unit for scanning the record carrier via a beam of electromagnetic radiation. The device is provided with clock means for generating a bit clock which, upon scanning of the track, is synchronous with the bit cells for writing and/or regaining the channel bits. Moreover, the device is provided with means for positioning the information blocks on a desired winding and angular position in the track. In concentric zones, a fixed number of information blocks per winding can be positioned per zone and the bit clock is constant so that the bit length in the zone increases from the inside to the outside. From zone to zone, the number of information blocks per winding increases. In another embodiment, the bit length and hence the information density is constant, and the information blocks of equal length are recorded one after the other in the track. The bit clock is generated in dependence upon the rotational speed and the radial position of the relevant winding. When a bit length is used which is minimally detectable during reading, a maximal average information density is realized.
A problem in the known system is that the position of information blocks in the track must be computed accurately. When using a constant density, the length of the track should be computed up to the desired position of, an information block, and the exact dimensions of the track must be included in a standard. When using zones, a large number of characteristic numbers must be taken up in a table in the form of a standard so that the characteristic numbers can be introduced in any other device. This renders a reading and/or writing device complex. Moreover, the standard with which the device and the record carrier must comply should comprise a large number of very, accurate data.
It is, inter alia, an object of the invention to provide a system comprising a record carrier and a device for reading and/or writing information of a high density, in which the position of an information block can be computed in a simple and accurate manner.
In accordance with a first aspect of the invention, a system as described in the opening paragraph for storing and reproducing information is therefore characterized in that the lengths of consecutive windings differ by an integral multiple and/or a rational fraction of the bit length.
In accordance with a second aspect of the invention, a record carrier of the type described in the opening paragraph is therefore characterized in that the windings on the record carrier are arranged at a track pitch Tp such that n*xcfx80*Tp=m*Bl, in which n and m are integers and are larger than or equal to 1.
In accordance with a third aspect of the invention, a device of the type described in the opening paragraph is therefore characterized in that the clock means are adapted to generate the bit clock in a predetermined relation with the track pitch Tp, such that m*Bl=n*xcfx80*Tp, in which n and m are integers and are larger than or equal to 1.
The inventive measures have, inter alia, the advantage that the number of bit cells preceding the position of the information block in a given winding of the track can be computed exactly when computing the position of an information block. In the case of an integral number of bit lengths per winding, the computation can be simply performed with integers, so that no rounding errors are produced. A rational fraction, for example 0.5, can also be processed in a computation in a simple and exact manner. Moreover, due to the use of an at least substantially constant bit length, the information density is maximal at given optical system parameters. Furthermore, there are no large discontinuities in the frequency of the bit clock. In the known system, these discontinuities occur at the transition between the zones and an ample distance between the information blocks is required for their compensation. In the system according to the invention, however, the appropriate bit clock can be computed easily and accurately at any radial scanning position.
The invention is also based on the recognition that, since the length of consecutive windings increases with 2*xcfx80*Tp at a track pitch Tp, the cumulated error over a large number of tracks without a rational proportion: between bit length and track pitch may differ in the computation in different devices in such a way that position deviations are produced, with information blocks partly overlapping each other. This leads to irreparable errors in the reproduction of the information.
An embodiment of the record carrier according to the invention is characterized in that a reference point is provided in the track at a radius R, such that the length of the winding from the reference point is an integral multiple and/or a rational fraction of the bit length. This has the advantage that the number of bit cells per winding can be exactly computed when the windings are counted from the reference point.
A further embodiment of the record carrier according to the invention is characterized in that the servopattern is provided with a modulation in which modulation disc information is coded, said disc information comprising track pitch information which is indicative of a ratio between the bit length and the track pitch. The ratio can be indicated with a limited number of bits by means of a number which is indicative of the ratio which is an integral number or possibly a simple rational fraction. This has the advantage that a device can read the relevant ratio from the record carrier without rounding errors. Moreover, several bit lengths may be used at a given track pitch in a simple manner in the system, while the device can always derive the bit length to be actually used from the track pitch information.
An embodiment of the device according to the invention is characterized in that the clock means are adapted to generate the bit clock during scanning of a part of the track in dependence upon a radius R on which a reference point is provided, the number of windings between the reference point and the part, and the track pitch. This has the advantage that the correct bit clock can be computed on the basis of known data, namely the length of a reference winding from the reference point at radius R, the winding number from the reference winding and the track pitch. Moreover, upon a jump to a new position, the bit clock can be computed already during the jump and set at the right value.
A further embodiment of the device according to the invention, in which the record carrier is provided with a servopattern which is indicative of the track, is characterized in that, while a predetermined number of synchronizing elements per winding is present in the servopattern, the clock means are adapted to generate the bit clock in dependence upon the synchronizing elements and the radial position of the winding. The rotational speed of the record carrier is generally controlled via a control loop on the basis of servo-information from the servopattern, while small deviations from the nominal speed may occur. The embodiment has the advantage that the bit clock is adapted to the actual rotational speed, so that the bit length is more accurate.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.